Constant gas flow regulating device

ABSTRACT

A constant gas flow regulating device includes an inlet chamber, an outlet chamber and a movable wall that delimits the inlet and outlet chambers from each other. The moveable wall carrics a body comprising an opening that permits communication between the inlet and outlet chambers. An elongate element extends centrally in the opening of the body in the moving direction of the wall. The opening within the body surrounds a portion of the elongate element. In a first position the opening in the movable wall is placed in the vicinity of a first end of the elongate element. The element has a sectional size that gradually increases from the first end to a second end thereof. The size of the opening in the movable wall is larger than the sectional size of the elongate element. A helical spring biases the movable wall towards a first position.

This is a U.S. National Phase Application Under 35 USC 371 and applicantherewith claims the benefit of priority of PCT/SE00/01323 filed Jun. 21,2000, which was published Under PCT Article 21(2) in English andApplication No. 9902377-2 filed in Sweden on Jun. 22, 1999.

TECHNICAL FIELD

The present invention relates to a constant flow regulating devicehaving an inlet chamber and an outlet chamber.

BACKGROUND OF THE INVENTION

Many diseases may be diagnosed by studying the concentration of certainsubstances, for example nitric oxide, in the exhalation air of a person.However, since the pressure of the exhaled air varies from person toperson, the volume of air passing through a test tube or the like perunit of time will vary considerably. There is therefore a need for adevice that will create a constant flow of exhaled air to a test tube orthe like independent of the pressure of the exhaled air. The object ofthe present invention is to provide such a device.

SUMMARY OF THE INVENTION

This object is obtained by a constant gas flow regulating device havingan inlet chamber and an outlet chamber, a movable wall delimits theinlet and outlet chambers from each other, said wall comprising anopening permitting communication between said chambers, an elongateelement extends centrally in the opening in the movable wall in themoving direction thereof, in a first position the opening in the movablewall is placed in the vicinity of a first end of the elongate element,said element having a sectional size that is gradually increasing fromthe first to a second end thereof, the size of the opening in themovable wall is larger than the sectional size of the elongate element,characterised in that a helical spring for biasing the movable walltowards a first position is provided and that a body attached to themovable wall and containing the opening surrounding a portion of theelongate element is slidably connected with an elongate guiding memberdefining the moving direction of the movable wall.

By such a device the space between the outer periphery of the elongateelement and the inner periphery of the opening in the wall will decreaseproportionally to the increase in pressure in the inlet chamber so thatthe pressure in the outlet chamber will be held constant independent ofthe pressure in the inlet chamber.

In the preferred embodiment the elongate element has a first enddisposed in the inlet chamber and a second end disposed in the outletchamber. The sectional shape of the elongate element corresponds to thesectional shape of said opening, the sectional shape of the opening inthe movable wall and of the elongate element being circular and theelongate element having the shape of a truncated cone. The movable wallcan be a diaphragm. Preferably the constant flow is in a range between0.5 and 4.5 1/min and more preferably between 0.6 and 3 1/min.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will now be described with reference to theenclosed Figure, which shows a sectional view of a preferred embodimentof a constant flow regulating device according to the invention.

DESCRIPTION OF AN EMBODIMENT

The device in the figure comprises a housing 11, the inner space of thishousing being divided into an inlet chamber 2 and an outlet chamber 3 bya diaphragm 4 of a flexible material, for example silicon rubber orlatex. A cylindrical hollow body 5 is attached to the diaphragm 4 and isextended from the diaphragm in the downward direction in the Figure. Thebody 5 has a it end which is situated in the inlet chamber 2 and asecond end situated in the outlet chamber 3.

A guide member 6 substantially in the form of a cylindrical body isextended centrally inside the housing 1 from a tube-shaped upper end 7thereof in the downward direction of FIG. 1. The guide member 6 issupported by the housing by any appropriate means permitting air to passthrough the tube end 7 into the inner space of the housing 1. The guidemember further comprises a seat element 8 in the form of an annularflange which is situated a distance from the upper wall of the housing1.

The hollow cylindrical body 5 has an inner diameter that is greater thanthe outer diameter of the guide member 6 so that an annular space existsbetween the outside of the guide member and the inside of the body 5.Furthermore, the first end of the body comprises means 9, for example atleast one guiding and connecting member, for slidably connecting thebody 5 with the guide member 6. The guiding and connecting member(s) caninclude three guiding pins or an annular sleeve. If an annular sleeve isused it should be connected to the main part of the body 5 by radiallydirected connecting pins or the like so that air can pass between thebody and the annular sleeve.

The second end of the body 5 contains a circular opening 10 with asmaller size than the inner diameter of the body 5 leading into theoutlet chamber 3. The opening 10 has a sharp edge and the walls of thebody 5 defining the opening 10 are diverging relative to each other fromsaid edge.

An elongate element 11 is extending downwardly from central part of thesecond end of the guide member 6. This element has a circular sectionalshape with a size that is increasing in the downward direction in theFigure. In the shown embodiment the element 11 has the form of atruncated cone. The element 11 and the member 6 are preferably made ofthe same material and integrated into a single piece of material.

Furthermore, a helical spring 12 is extended between the diaphragm 4 andthe lower wall of the housing 1. The body 5 is by this spring 12 biasedtowards a first position in which the first end thereof is seatedagainst the annular flange 8 of the guide member 6. The diaphragm isreinforced by a rigid annular plate in the central area so that thespring 12 acts against this annular plate 14.

The device described above functions in the following way. Before usethe pressures in the inlet and outlet chambers are equal and the body 5is situated in the first position. When air exhaled by a person flowsinto the inlet chamber 2 via the inlet tube 7 the pressure in the inletchamber becomes greater than in the outlet chamber, the pressuredifference causing the diaphragm and thereby the body 5 to movedownwards against the force of the spring 12. The exhaled air can thenpass through the space between the outside of the element 11 and theedge of the opening 10 in the second end of the body 5 into the outletchamber 3.

However, due to the pressure drop over the passage between the inlet andthe outlet chamber, a difference in pressures between the chambers willalways exist, the pressure in the outlet chamber being less than in theinlet chamber. In the Figure, the body 5 has moved downwards from thefirst position pressing against the seat 8 and the exhaled air flowinginto the inlet chamber 2 flows in the passage between the edge of theopening 10 and the outside of the elongate element 11, into the outletchamber 3 and leaves this chamber through openings 13 therein, as isindicated by arrows in the Figure.

The greater the pressure in the inlet chamber is, the longer distancewill the body travel 5 in the downward direction in the Figure. However,the longer distance the body 5 will travel, the smaller the spacebetween the edge of the opening 10 and the outside of the elongateelement 11 will be. Thus, the higher the pressure in the inlet chamber,the smaller the passage between the inlet and the outlet chambers willbe The space between the outside of the element 11 and the edge of theopening 10 will thus define an annular regulating opening with a varyingsize dependent of the pressure in the inlet chamber.

By rightly dimensioning the increase in sectional size of element 11 inthe downward direction, the pressure drop over this regulating openingcan be made to increase with pressure in such a way that a constant flowof air passes through this regulating opening for varying pressures inthe inlet chamber. The pressure drop over this regulating opening neededfor maintaining a constant pressure in the outlet chamber and the sizeof the regulating opening for obtaining such a pressure drop isrelatively easy to calculate. Its also relatively easy to calculate themovement of the body 5 in dependence of the pressure difference betweenthe inlet and outlet chambers for varying inlet chamber pressures and independence of the force of the helical spring 12 and thereby thesectional increase in size of the element 11 is relatively easy tocalculate.

For a constant flow regulating device for maintaining a constant flow ofexhaled air out of the outlet chamber 3 through openings 13 in thehousing 1 for a pressure in the inlet chamber varying between 500-2000Pa and with an opening in the body 5 having a diameter of 3.5 mm and alinear helical spring with a spring constant of 250 N/m, a cone angle of{fraction (1/70)} of the elongate element 11 will make the pressure inthe outlet chamber 3 independent of the variation pressure in the inletchamber 2 within the above mentioned limits and with the requiredaccuracy.

The helical spring is pretensioned to a force corresponding to apressure of 500 Pa in the inlet chamber 2 and the body 5 will thus notmove until the pressure in the inlet chamber exceeds 500 Pas. If thepressure in the inlet chamber exceeds 2000 Pa, the body 5 have travelledalong the elongate element 11 to a point thereof when the sectional sizeof the element is equal to the diameter of the opening 10 and thepassage between the inlet and the outlet chambers is then closed.

For the described embodiment, the calculations mentioned above led to anelongate element having a linear increase in sectional size. Such anelement is easy to manufacture However, for other parameters thecalculations may lead to an elongate element that gradually increases insectional size along a curve. The sectional shapes of the opening in thediaphragm and the elongate element need not necessarily correspond toeach other or be circular. However, if those shapes correspond to eachother and are circular, the calculations are facilitated and the flow ofair through the regulating opening will be more undisturbed.Furthermore, the passage between the inlet chamber and the outletchamber can not be closed when the pressure in the inlet chamber exceedsthe maximum pressure allowed if the shapes of the opening in thediaphragm and the sectional shape of the elongate element differ fromeach other. A circular shape of the opening in the diaphragm and acircular sectional shape of the elongate element is therefore preferred.

Example introduced during the priority interval

Another example of a flow regulating device has a diaphragm of 44 mmwith an opening of 3.2 mm and a linear helical spring with a springconstant of 66 N/m. The elongate element has a cone angle of 1:42.5 andthe gap between the diaphragm and the elongate element will vary between0.17-0.10 mm when the pressure varies between 500-2000 Pa. This willgive a constant flow of 2.7 1/min.

In order to facilitate the manufacturing of the elongate element and toobtain the required accuracy, the cylindrical body should be allowed totravel at least a distance twice the diameter of the smallest diameterof the elongate element.

All parts of the described flow regulating device except the spring andthe diaphragm are preferably made of plastic material, for examplepolyamide, polyprophene or polyethene. However, metal materials can alsobe used.

The device is shown in the figure with the moving direction of themovable wall 4 being downwards-upwards. However, the described devicewill function in the same way independent of placement of the housing.

The described embodiment can of course be modified in several wayswithin the scope of the present invention. The diaphragm could forexample be made of a resilient material in which case the helical springcan be deleted. In such a case it is important that the material of thediaphragm is reinforced in the area surrounding the opening therein sothat the dimensions of the opening will not change during the elasticsketching of the diaphragm. The movable wall need not be a diaphragm butcould be a rigid wall slidably supported in the housing. However, adiaphragm is preferred since air tightness between the outer edge of thediaphragm and the wall of the housing is easy to accomplish Furthermore,the spring could be seated against the second end of the cylindricalbody 5 instead of pressing against the rigid part of the diaphragm as inthe shown embodiment. The housing can have another shape than in theFigure and other guiding means can be used for guiding the body 5, forexample a perforated guiding sleeve disposed in the outlet chamber cansurround the body 5, the scat element defining the first position of thebody then being separate from the guiding member and placed in the inletchamber. However, the shown guiding means are preferred since theelongate element, the seating for the cylindrical body and its guidingmeans can be integrated in a single piece of material. The scope of theinvention shall therefore only be restricted by the content of theenclosed claims.

What is claimed is:
 1. A gas flow regulating device, comprising: aninlet chamber; an outlet chamber; a movable wall delimiting the inletand outlet chambers from each other; a body comprising an opening, saidbody being moveable with said wall; a fixed elongate element extendingcentrally in the opening of said body in the moving direction of saidmoveable wall, thereby defining an annular space between a portion ofthe elongate element and the opening that permits communication of gasbetween the chambers, said elongate element having a first end disposedin the inlet chamber and a second end disposed in the outlet chamber,and having a sectional size gradually increasing from its first end toits second end; a helical spring for biasing the movable wall towards afirst position where the movable wall is placed such that said openingof said body is located in the vicinity of the first end of the elongateelement; and said body being attached to the movable wall and containingthe opening surrounding said portion of the elongate element, at leastone guiding and connecting member slidably connecting said body with afixed elongate guiding member for guiding the wall when moved, wherein,when the gas pressure increases in the inlet chamber, the wall is movedfrom said first position towards the second end of the elongate element,thereby gradually decreasing the size of said annular space between theopening and the elongate element, so as to obtain a constant gas flowfrom the inlet chamber to the outlet chamber independent of pressurevariations in the inlet chamber.
 2. The device according to claim 1,wherein the body is seated against a seat element in the first position.3. The device according to claim 2, wherein the seat element comprisesan annular flange provided on the guiding member.
 4. The deviceaccording to claim 1, wherein said at least one guiding and connectingmember comprises a plurality of guiding pins.
 5. The device according toclaim 1, wherein said at least one guiding and connecting membercomprises an annular sleeve.
 6. The device according to claim 1, whereinthe sectional shape of the elongate element corresponds to the sectionalshape of the opening.
 7. The device according to claim 6, wherein thesectional shape of the opening and the elongate element, respectively,is circular.
 8. The device according to claim 1, wherein the elongateelement has the shape of a truncated cone.
 9. The device according toclaim 1, wherein the movable wall includes a diaphragm.
 10. The deviceaccording to claim 9, wherein the diaphragm is reinforced by a rigidannular plate, and wherein the helical spring acts against said plate.11. The device according to claim 1, wherein the guiding member isdisposed in the inlet chamber and the elongate member extends from theguiding member.
 12. The device according to claim 11, wherein theguiding member and the elongate element are integrated into a singlepiece of material.